1. Field of the Invention
This invention generally relates to an arrangement for and a method of supplying electrical power from an external electrical power source to a battery-powered electrical device such as an electronic flash unit and, more particularly, to a lockable power module insertable into a battery compartment of the unit and reliably locked in position within the compartment.
2. Description of Related Art
Photographers using battery-powered electronic flash units as camera accessories often resort to portable external rechargeable battery packs to power the flash units. Such rechargeable battery packs typically provide, better performance and delivery more electrical energy in a shorter time, as compared to individual dry cell batteries. Many photographers often do not want to be bothered with replacing individual batteries, and certainly commercial photographers do not want to be faced with a failing or depleted power source during a photographic session.
In order to supply electrical power from a rechargeable battery pack to a battery-powered flash unit, it is known to remove the individual batteries that normally power the flash unit from a battery compartment provided in the unit, and to insert a so-called power module into the compartment after the batteries have been removed. A twin-wire cable has one end connected to the module and an opposite end furnished with a connector. The connector is plugged into the rechargeable battery pack, thereby conducting electrical power from the pack to the flash unit when the power module is inserted into the compartment.
Although generally acceptable for its intended purpose of supplying power to the flash unit, the known power module has not proven to be altogether reliable in practice. The use of a cable and its associated external battery pack has resulted in an awkward, non-reliable connection of the power module in the battery compartment. The battery compartment of most flash units is typically closed by a door that is either hinged to, or slidable on, the flash unit. When either the hinged or sliding door is closed, the door serves the important function of pressing the anodes and cathodes of the individual batteries into affirmative engagement with electrical power terminals located on a bottom wall of the battery compartment, thereby insuring a reliable electrical connection.
However, when using the external battery pack, the presence of the cable has interfered with the aforementioned pressing function of the door because the door could not be fully closed without pinching or otherwise damaging the cable. Failure to fully or properly close the battery compartment door compromised the reliability of the electrical connection between the power module and the flash unit because, simply put, the partially open door no longer reliably held the power module in the compartment. Under certain circumstances, the power module could fall out of the battery compartment due to the improperly or incompletely closed door.
To avoid this unreliability problem, some photographers have cut a notch in the door to allow the cable to exit. The door could now be closed and also could provide at least some pressure against the power module. However, many photographers are reluctant to cut irreparable portions out of their flash units, not only because the trade-in value of so-damaged flash units is decreased, but also because of the degradation in appearance due to such unsightly notches.
Other photographers have simply made the best of a bad situation and partially closed the battery compartment door, leaving only enough room for the cable to exit. In this event, the door must be held ajar by some means, typically adhesive tape or hook-and-loop-type fasteners in order to position the door to apply pressure on the module and, in turn, on the electrical terminals within the battery compartment. However, this modification is an inelegant solution since the partially-open door is always prone to being fully open, depending on the reliability of the holding power of the adhesive or fasteners used. Also, a partially-open door is esthetically unattractive.
Since different flash units are formed with differently sized battery compartments, the manufacturers of power modules have had to design their modules with a compromise size suitable to fit within several battery compartments of different sizes. Needless to say, an undersized power module for an oversized battery compartment tends to undesirably shift within the same, bounce repeatedly against the partially-open door, and is more likely to fall out of the compartment.